Typically, air cargo containers, often referred to as Unit Load Devices (ULDs) are shaped as boxes which can include appropriately sloped surfaces that conform the air cargo container to the aircraft's fuselage when the air cargo container is placed in the aircraft's cargo compartment. ULDs meant to be loaded into an aircraft's lower deck cargo compartment—lower deck containers—in general are equipped with sloped lower side walls, joining the edge of the base to the vertical upper side walls. Upper deck containers on the other hand have sloped upper side walls and vertically upward extending lower side walls attached to the ULD's base panel.
Essentially, the container is made of several panels which are joined together to form the air cargo container and define an enclosed or partially enclosed volume. Additionally, an air cargo container typically has a door which allows it to be opened for placing e.g. cargo or baggage in the air cargo container or for removing the payload from the air cargo container. Air cargo containers must conform to various national and international standards and specifications. These standards and specifications are set forth in amongst others the National Aerospace Standard (NAS) 3610 and the International Air Transport Association (IATA) ULD Technical Manual. In these documents, the required characteristics of air cargo containers, such as for instance the ability to sustain defined vertical and lateral loads and impacts, shear forces and fire resistance are set out. Likely the most severe load criterion is the downward load case. In case of an upper deck container, the vertical downward load is exerted fully on the base panel of the container. In case of a lower deck container on the other hand, the vertical downward load is partially exerted on the base, and partially on the—sloped—lower side walls. Heavy loading of the sloped lower side walls may result in substantial deformation.
Presently there are roughly two known types of air cargo containers. The first and most common type is equipped with a so-called shear panel that spans over part of the front surface of the air cargo container to obtain the necessary stiffness, and as such forms an integral part of the container's structure. The remaining part of the front surface is used as access opening. To close the opening off when loaded, a flexible fabric door spanning the opening may be used. An air cargo container of this type is disclosed in U.S. Pat. No. 5,109,998 for instance. Another air cargo container having a shear panel is disclosed in U.S. Pat. No. 5,941,405, which shows a collapsible container having a shear panel in the form of an outboard wing or ‘pallet extension’. The pallet extension extends outwardly of the container base so that the container assumes a so-called ‘LD3’ unit load device configuration. As can be seen in FIG. 1 of U.S. Pat. No. 5,941,405, the pallet extension 26 blocks a part of the available maximum opening surface area, which is undesirable. Another example of this type of container is disclosed in DE 20214619U1, see FIG. 1, and in EP0127936 A1, see FIG. 1. EP 1061009A1 discloses a further example of a collapsible container having a shear panel to obtain the necessary rigidity. As is clear from FIG. 1 of EP 1061009A1, the shear panel blocks part of the front opening extending between walls 4, 8, 7 (and 5, 6).
A second type of air cargo container is equipped with a solid door, often constructed from aluminium or an aluminium alloy and comprising a top and bottom part, connected by a hinge. This type of air cargo container is for instance known from GB 1470448.
Air cargo containers with a solid door provide the required rigidity but are significantly heavier than those with a flexible fabric door. Air cargo containers with a flexible door are lighter but require a shear panel to provide the necessary rigidity. The shear panel necessarily blocks part of the available opening however, and access to the interior of the container is therefore limited. This reduced access hinders loading and offloading and may lead to important time losses, in particular when using mechanical loading and offloading devices. Also, such mechanical devices may not always be suitable for use in conjunction with containers equipped with shear panels.
It would be highly desirable to provide an air cargo container combining the advantages of the container having a flexible door (low weight) and of the container equipped with a solid door (allowing optimal access to the entire interior of the air cargo container), and at the same time providing sufficient structural rigidity to comply with the abovementioned standards and specifications. This is particularly the case for so-called (half width) lower deck aircraft containers, having sides sloping outward and upward from the base—to which it is restraint.